The present invention relates to an IC socket which is used to connect PGA (pin grid array) ICs (integrated circuits) that have pin contacts arranged in the form of a matrix to circuit boards.
Ordinarily, IC sockets which are used to connect PGA ICs that have pin contacts arranged in the form of a matrix to circuit boards have numerous contacts. BGA (Ball Grid Array) sockets have been developed in which solder balls attached to the respective contacts are soldered to the circuit board by being heated all at one time.
Here, an epoxy resin containing glass fibers is widely used as the resin that forms the circuit board, and an insulating resin such as a PBT (polybutylene terephthalate) is commonly used for the housing that holds the contacts. However, since these two resins have different linear expansion coefficients, a load is applied to the solder balls after the IC socket is mounted on the circuit board, and this causes solder cracking, resulting in electrical discontinuities between the IC and the circuit board. Furthermore, as a result of the difference in linear expansion coefficients, warping tends to occur in the connector main body and board, and when stress is applied to the soldered parts as a result of this warping, there is a danger of breaking of the electrical continuity.
Accordingly, a technique in which thermal expansion and thermal contraction absorbing parts are formed in the housing is disclosed in the invention of Japanese Patent Application Kokai No. S62-37887. In this application slits 150a which extend from one wall part toward the interior of the housing 120 in the short direction of the housing 120, and slits 150b which have the same depth as the slits 150a and which extend from the other wall part toward the interior of the housing 120, are alternately formed between specified rows of contacts 130 as shown in FIG. 6(A). Slots 151 which are larger than the diameter of the contacts 130 are formed between specified rows of contacts 130 as shown in FIG. 6(B).
As a result of, the difference in linear expansion coefficient between the housing and the board is absorbed, so that solder cracking tends not to occur. Furthermore, warping of the connector and board also tends not to occur.
However, the slits 150a and 150b and slots 151 are formed so that they pass entirely through the housing 120 from the upper surface to the lower surface. Not only is the strength of the housing 120 compromised, but the flow of the synthetic resin that constitutes the molding material is poor when the housing 120 is molded, so that it is difficult to manufacture a housing that has the desired shape.
Accordingly, an object of the present invention is to provide an IC socket which can prevent the occurrence of solder cracking and warping by absorbing the difference in linear expansion coefficient between the housing and board without lowering the strength of the housing.
In order to address theses problems, an IC socket is provided in which contact receiving cavities accommodate the securing sections of contacts arranged in the a matrix. The cavities pass through the upper and lower surfaces of a housing. Pin receiving openings are formed in the upper surfaces of the contact receiving cavities. Solder ball receiving cavities are formed in the lower surfaces of the contact receiving cavities, so that these pin receiving openings and solder ball receiving cavities are opened wider than the contact receiving cavities. This IC socket further featuring first slits which have a bottom, and which extend from the upper surface of the housing toward the undersurface of the housing, between specified rows of the pin receiving openings. Second slits having a bottom, and extending from the undersurface of the housing toward the upper surface of the housing, are formed between specified rows of the solder ball receiving cavities in positions where the first slits are not formed.